Technical Field
The present invention relates to a displacement measurement device and a method of measuring displacement utilizing optical interference.
Background Art
Patent Document 1, for example, discloses a displacement measurement device that utilizes optical interference. This displacement measurement device includes, in order from a light source side, a laser light source, a collimator lens, a first diffraction grating, a second diffraction grating, and an optical sensor. The optical sensor detects interference between diffracted light (first-order diffracted light, for example) diffracted by the first diffraction grating and diffracted light (first-order diffracted light, for example) produced when the second diffraction grating diffracts the zero-order light that passes directly through the first diffraction grating. The displacement measurement device measures changes in the distance between the first and second diffraction gratings (which correspond to the target displacements to be measured) according to changes in the intensity (brightness) of the interference light detected by the optical sensor (see paragraphs [0020], [0023], [0027], and FIGS. 1 to 3 in Patent Document 1, for example).
Patent Document 2 discloses an optical encoder that includes a first slit plate, a second slit plate arranged facing the first slit plate, and a sensor connected to the second slit plate. The pitch of the slits in the second slit plate is less than the pitch of the slits in the first slit plate. The sensor detects light that passes through both the first and second slit plates as the second slit plate is moved relative to the first slit plate and generates pulse signals according to this detected light (see paragraph [0011] and FIG. 3 in Patent Document 2, for example).